A hard disk drive generally includes one or more rotating disks or platters and a spindle motor that is controlled to cause the disks to rotate. Data is generally stored in the form of a sequence of magnetically polarized regions on the surface of the disk. One or more read/write heads, which is sensitive to changes in magnetic flux, reads and/or writes data to the disks as it is supported by an arm above the surface of the disks in close proximity relative to the disks. An actuator motor (typically a “voice coil motor” or VCM) controls the positioning of the arm for moving read/write heads relative to the surface of the disks.
As a disk rotates under the read/write head, the read/write head “flies” on a thin cushion of air created by the motion of the disk. The read/write head reads data from a disk by sensing flux changes on the magnetic surface of an associated disk as it passes beneath the read/write head. Various types of disk drives include several disks, each surface of which has an associated read/write head. The read/write head includes a small coil (or winding) of wire through which current flows to read or write data relative to the disks. The head employs an inductive coil to generate magnetic fields, which form magnetic patterns on the medium representing the binary data (e.g., ones and zeros). The orientation of the patterns depends on the direction of electrical current flow through the inductive coil. That is, writing binary data entails selectively changing, or reversing, the direction of current flow through the head. The direction of current flow through the coil is the controlled by a write driver. In order to write data, the write driver drives electric current through the write head to create a temporary magnetic field which magnetizes a small region of the disk at the current position of the write head.
When the write driver activates write current, it is desirable that little or no overshoot occur. If large overshoot of the write current occurs, data can be overwritten to an adjacent track. A short settling time of the write current to its final (steady state) value also is desirable after it is turned on. For example, a short settling time enables bits of data to be packed more closely, which can improved the data density per track.